Bladder cancer (BC) is one of the 10 most common cancers in the world, and its recurrence and metastasis are the main causes of death in BC patients. Exploring the molecular mechanisms of BC pathogenesis and searching for new prognostic markers and therapeutic targets are important for improving patient prognosis. KPNA2 was found to be a potential oncogene in different malignant tumours, as demonstrated in our previous study. To better understand the mechanisms associated with BC development, we investigated the inhibitory effect of miR-20a-5p on the oncogene KPNA2. RNA-seq data from BC patients were downloaded through the TCGA database for bioinformatics analysis, including gene expression, co-expression analysis, GSEA, nomogram modelling, functional enrichment analysis, WGCNA, GO and KEGG to assess the potential biological functions of miR-20a-5p in BC. Subsequently, we further verified the expression of miR-20a-5p in BC cells by RT-qPCR, and in vitro experiments were performed to investigate the effects of this gene on BC cell proliferation and migration. MiR-20a-5p was downregulated in BC tissues and cells. Kaplan-Meier analysis revealed that the higher the expression of miR-20a-5p in patients, the higher the survival rate of BC patients. MiR-20a-5p overexpression inhibited the proliferation and migration of BC cells. In addition, miR-20a-5p can directly bind to nuclear transporter protein α2 (KPNA2) in cells, targeting and regulating the expression of KPNA2. These findings indicate that miR-20a-5p targeting KPNA2 adversely affects the proliferation and migration of BC cells, suggesting that miR-20a-5p may be an attractive target in BC therapy.